This invention is concerned with improvements relating to mining machinery, particularly but not exclusively for cutting coal, in which context the invention will hereinafter be described.
A conventional coal cutting machine as used for example for mining coal comprises a cutting head provided with a number of picks secured thereto. Where the cutting head is of the kind having a number of helically-extending vanes (as for example is the case where the cutting head is in the form of a shearer drum) the picks are secured to the vanes so as to attack the coal face as the cutting head is rotated.
Conventional practice is for housings for the picks to be fixedly secured to the vanes of the cutting head by for example a welding operation, and the picks to be releasably secured in the housings with an operative portion protruding therefrom. Such housings are known in the art, and will be referred to hereinafter, as pick boxes.
There are several different types of pick which are designed to attack the coal face in different ways, and normally a cutting head will utilise several different types of pick at different positions around its periphery, in accordance with the type of material being cut. For each type of pick there is conventionally a corresponding type of pick box, into which the pick may be releasably secured.
When a pick becomes worn or broken, a greater load is thrown on the immediately following pick: thus, it is desirable to replace a broken or worn pick as soon as possible. If however, during operation of the cutting head one of the pick boxes becomes damaged, it may be difficult to replace the pick within that box. Thus, when damage is caused to a pick box it is necessary to cut the pick box from the cutting head and to replace it with another pick box.
This is a difficult and time consuming operation, and cannot easily be carried out insitu. Normally replacement of a damaged pick box involves ceasing operation of the machine for an extended period of time, and taking the machine out of service. Thus, and especially where personnel operating the machine are working under a production incentive bonus, there is a tendancy for a broken pick to be left in position, where extraction of the picks from the pick box, and replacement thereof with a new pick, is rendered inpractical due to damage incurred by the pick box.
Primarily this practice is disadvantageous in view of the increased loading placed on the immediately following pick, and consequent increased rate of breakage of said following pick, and an increased utilisation of fresh picks. Additionally, however increased loading is also placed on the box housing the immediately following pick, and consequently a decrease in the life of this pick box.
In normal workings, it will not be until an excessive number of pick boxes are damaged, as causes noticeable impairment in the cutting effeciency of the machine, that the machine will be shut down and all damaged pick boxes replaced. Such practice greatly increases the rate of utilisation of picks and pick boxes, albeit this is offset to some extent by continuing operation of the machine.
It is one of the various objects of this invention to alleviate this problem to some extent at least.